The present invention relates to a valve clearance adjustment for improving smoothness of an idle operation of a multi-cylinder internal combustion engine, and more particularly to a method of and an apparatus for effecting a valve clearance adjustment for improving smoothness of an idle operation of a multi-cylinder internal combustion engine. The present invention also concerns an indicator device for indicating a crankshaft angle where adjustment of a valve clearance is to be conducted.
In a certain conventional multi-cylinder internal combustion engine, it is necessary to conduct adjustment of a valve clearance for each of intake and exhaust valves in order to compensate for a change in a valve clearance.
A conventional valve clearance adjustment method is described hereinafter taking a reference to FIGS. 10-12. FIGS. 10 and 11 show a front end portion of a conventional multi-cylinder internal combustion engine including a crankshaft pulley 1 fixed to a front end of a crankshaft. On the outer peripheral portion of the pulley 1 is a TDC mark 2. On a stationary member in the form of a timing belt cover 3 is a timing indicator 4. When the TDC mark 2 meets with the timing indicator 4 as is the position shown in FIGS. 10 and 11, the engine crankshaft assumes a crankshaft angle where one of the engine cylinders, for example, No. 4 cylinder, is at its compression top dead center. In the case of a four cylinder in-line internal combustion engine, No. 1 cylinder is at its compression top dead center after rotating the crankshaft through 360.degree. from the above-mentioned crankshaft angle position. These crankshaft angles are conventionally selected as positions where adjustment of a valve clearance is conducted.
The valve clearance adjustment schedule is more precisely described taking a reference to FIG. 12. In this Figure, positions where intake and exhaust valves are adjusted are designated. For example, NO. 1 IN designates a compression top dead center where the intake valve in No. 1 cylinder is to be adjusted. Describing in detail, at the compression top dead center of No. 1 cylinder where both the intake and exhaust valves in this cylinder are seated, the valve clearance adjustment is conducted on the intake and exhaust valves in No. 1 cylinder, the intake valve in No. 2 cylinder, the exhaust valve in No. 3 cylinder. Subsequently, at the compression top dead center of No. 4 cylinder when the TDC mark 2 meets again with the timing idicator 4 after rotating the crankshaft through 360 degrees, the valve clearance adjustment is conducted on the intake and exhaust valves in No. 4 cylinder, the exhaust valve in No. 2 cylinder, and the intake valve in No. 3 cylinder.
Referring back to FIGS. 10 and 11, the above-mentioned crankshaft pulley 1 is provided also with six pulley marks 5 which are angularly spaced by 5.degree. from the TDC mark 2. The pulley marks 5 are used during inspection and adjustment of ignition timing in the No. 1 cylinder.
A problem caused by this conventional valve clearance adjustment method is explained.
For lifting the intake and exhaust valves in accordance with a predetermined schedule determined with respect to crankshaft angle of the engine crankshaft, a valve train for the above-mentioned four-cylinder in-line engine includes a single camshaft for activating both intake and exhaust valves. When the intake or exhaust valve is being lifted, the reaction due to compression of a valve spring acts on the camshaft via a rocker arm, causing a deflection of the camshaft. Thus, when the exhaust valve in one cylinder is lifted, a valve clearance provided for the adjacent intake valve in the same cylinder increases more than it does when the associated exhaust valve is not lifted.
FIG. 13 shows a valve lift diagram of each of the intake and exhaust valves in No. 1 and No. 4 cylinders when the valve clearance adjustment is conducted at the compression top dead center position of the No. 1 cylinder and at the compression top dead center position of the No. 4 cylinder in accordance with the conventional method. The valve lift is measured in terms of the lift of a rocker arm of the associated valve. In this Figure, EO designates an opening timing of an exhaust valve, EC designates a closing timing of an exhaust valve, IO designates an opening timing of an intake valve, and IC designates a closing timing of an intake valve. A valve clearance is adjusted to 0.30 mm at 80.degree. C., and the measurement is made at 80.degree. C. It has been confirmed that an increase in the valve clearance is substantially noticeable immediately before and after the valve overlap in the No. 4 cylinder. As a result, the valve overlap in the No. 4 cylinder is less than that in the No. 1 cylinder by 10.degree. as will be readily understood from FIG. 13. Thus, the No. 1 to No. 4 cylinders produce uneven torque, causing unstable idling of the engine.
In the above-mentioned example, the virtual valve clearance of each of the intake and exhaust valves in each of the No. 1 cylinder and No. 4 cylinder is increased as compared to that at the time of the valve adjustment. This causes the valve overlap to vary. This variation in the valve overlap due to the resilient deflection of the camshaft is not even over all of the cylinders, thus bringing about an uneven overlap among the cylinders. This results in instable idling of the engine.
An object of the present invention therefore is to provide a valve clearance adjustment method which improves smoothness of an idle operation of a multi-cylinder internal combustion engine.
Another object of the present invention is to provide an indicator device to be used for carrying out the above-mentioned valve clearance adjustment method.